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Project Title: Scale Effect and Surface Characterization of Cementitious Materials

Sponsored by: National Science Foundation

Research Objectives:

• Study the influence of micro-structural parameters, such as aggregate size, and macroscopic parameters, such as specimen size, on the fracture toughness of brittle materials.
• Suitability of modified slit island method which uses area-perimeter relation in computing fractal dimension for concrete fracture surface characterization.
• Development of constitutive model of brittle fracture for extrapolating the small scale testing results to large structural elements.
• Reliability prediction of brittle materials.

Accomplishments:

• Over 300 wedge-splitting concrete specimens of various sizes ((width x total depth x thickness) 105 x 105 x 12.5 mm to 1680 x 1680 x 200 mm.) with various maximum aggregate sizes (4.75, 9.5, 19, 38, 76 mm) were tested.
• Fracture parameters such as, stress intensity factor, energy release rate, fracture energy and crack opening displacements were computed and compared.
• Fracture surfaces were characterized by fractal dimension technique.
• Probabilistic analysis were performed on the experimental results.
• Size effect and reliability prediction equations were proposed.

Fig.11 Set of specimens	Fig.12 Typical test setup
Fig.13 Islands in fractal analysis